tkgg1
幼苗
共回答了17个问题采纳率:94.1% 举报
x=13/(4-√13)
x=13(4+√13)/(4-√13)(4+√13)
x=13(4+√13)/3
y=13/(4+√3)
y=13(4-√13)/(4+√13)(4-√13)
y=13(4-√13)/3
3x²+5xy+3y²
=3x²+6xy+3y²-xy
=3(x²+2xy+y²)-xy
=3(x+y)²-xy
=3[13(4+√13)/3+13(4-√13)/3]^2-xy
=3(104/3)^2-13(4+√13)/3*13(4-√13)/3
=104^2/3-13^2/9*3
=104^2/3-13^2/3
=1/3*(104+13)(104-13)
=1/3*117*91
=39*91
=3549
1年前
7